The purpose of this study is to determine the extent to which body fat, regional distribution of fat, and fitness influence growth hormone (GH) secretion in young, middle-aged, and older adults. These relationships will be examined during spontaneous, fasting and exercise conditions. Body composition will be determined using a 4 compartment model and GH section by frequent sampling. We will also investigate whether the decrease in GH secretion with aging is due to a decrease in GH pulse frequency, amplitude, or some combination of these factors. A total of 38 subjects have completed all admissions; will not study 20 middle-aged subjects; abstract submitted to Endo Soc 97, manuscript reporting control data and body composition measurements in preparation.